DUONG Phu-Hiep duongphuhiep

How to Review PRs (or MRs) of unfamiliar C# codes base?

If you have to review a Pull (or Merge) request in an unfamiliar C# Code bases, what will you check? Here is "my method" (or check list) to review a C# codes base without knowing what it is doing.

As we don't know much about what the code is doing, we can only review on the "best pratice" aspect:

where are the tests which would cover all the changes? justify if the changes are not unit-testable (yes, it can happen)
challenge if there are unjustified try / catch
challenge if "Generic" or "Reflection" are used (over-engineering smell)

Logging best practices

When generate a log message

Major branching points in your code
When errors or unexpected values are encountered
Any IO operations: calling database / stored proc or make http request
Significant domain events
Request failures and retries
Beginning and end of time-consuming operations

Problem

Your HTML page (the host page) has an Iframe. The Iframe source is on other domain, so you will have to use the window.postMessage() for cross-origin communication. But this communication is only in 1 direction (The Iframe can inform the Host or the Host can inform the Iframe)

This article shows you how to make the Request/Reply communication using postMessage() and MessageChannel combination.

The article did not show you how to add a timeout to the communication, so the Iframe might wait forever if the Host did not response.

I will resume the technique by some codes snippets and at the same time add the missing timeout implementation.

Technical Errors vs Business Errors

API's designer often categorize errors into "Technical" and "Functional" (or "Business") errors. However, this distinction may not make sense:

An API/micro-service should always return ONLY "Functional" (or "Business") errors.
The API/micro-service migh be crashed while processing a consumer's request and so the consumer will naturally get a technical error. But the API/micro-service should not deliberately return a "Technical" error for consumer. The simple fact that the App built a nice response called "Technical error", then gracefully return it, make it no longer a technical error, but a "fake" one.

We will explore the distinction between "real technical errors" and "fake technical errors". "Fake technical errors" are initially technical but later manifest as business errors, thus becoming "fake technical errors."

HTTP 404 Business error (or Fake technical error)

Read Part 1: MediatR vs MassTransit Mediator - Differences

The MassTransit Mediator implementation is more powerful than MediatR implementation, but also more complicate to use. Unit Testing a MassTransit Consumer is not a nice experience.

In this article I will propose some techniques to simplify the MassTransit Consumer and to make them look as straight forward as a MediatR handler.

Case study

We will study a very common use case (the most common use case which I can think of):

Why mediator?

In a ASP.NET Web application. You don't need mediator

If you prefers to make controlers depends directly to the Application Codes instead of indirectly via the Mediator.
If you prefers to make a normal ASP.NET Web Application instead of a Mediator Application

Frankly it is not a Bad choice, no need to use a Mediator framework or make a Mediator Application just because everyone did.. Though, There are benefits in making a Mediator Application:

Event sourcing (Messages broadcast), CQS pattern..
Decouple the Controler (presentation) from Application codes, so that you could swap the presentation technology. For eg, if you make a "MassTransit" application, then you can swap the presentation layer to Mediator or RabbitMQ, or Grpc.. => you are not to be sticked with or limited by ASP.NET presentation => but rather sticked with and limited by your mediator framework!

	using System.Security.Cryptography;
	using System.Text;

	namespace Lemonway.TransactionService.Application
	{
	public static class AesEncryptionHelper
	{
	public static string Encrypt(string payload, string secret)
	{
	byte[] iv = new byte[16];

	// Place your key bindings in this file to override the defaultsauto[]
	[
	{
	"key": "ctrl+t",
	"command": "workbench.action.togglePanel"
	},
	{
	"key": "ctrl+shift+f4",
	"command": "workbench.action.closeOtherEditors"
	},

	using MassTransit;
	using MassTransit.Testing;
	using Microsoft.Extensions.DependencyInjection;
	using Moq;
	using Moq.AutoMock;
	using System.Threading.Tasks;
	using Xunit;

	namespace HiepTest;